Most of the time people are probably making assumptions that may not be true. However, I think a new house counts. While borrowing is cheap, more new houses are built, and the competition for land for new houses pushes up prices. So it's possible it has skme impact, but it really depends on how exactly NZ (Stats NZ?) counts it. I would expect the land value to not be included but maybe it is, I haven't managed to find a list of what is and isn't included in GDP.

Rising housing costs are counted in inflation numbers, though.

Edit: you may be right about capital gains, it means more spending money for the sellers (and the buyers pay with debt so the drop on that side is delayed)